Method for recording holographic images of human subjects

ABSTRACT

A method for recording lifelike images of human subjects comprises the steps of illuminating the subject with a light source of substantially the same color as the wavelength of the laser to thereby simulate the laser for at least a predetermined time period necessary to adapt the subject&#39;s eyes to the intensity level of the light source; extinguishing the light source; opening the shutter; and activating a pulse laser, wherein the extinguishing, opening, and activating steps are performed within a time period of approximately 0.5 seconds.

This application is a division of application of Ser. No. 327,180 filedDec. 3, 1981, now U.S. Pat. No. 4,474,421.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

This invention relates to a method for recording holographic images ofhuman subjects safely and in a manner whereby dark eye adaptation of thesubject is minimized and to obtain the recording of more lifelike humanimages.

2. Description of the Prior Art

The recording of images by a holographic process necessarily requires alaser source to generate the object beam and the reference beam. Theenergy generated by a laser must be of sufficient intensity to record aholographic image on a holographic film plane.

Particularly when the object being recorded is a human subject, thegeometries of the object and reference beam paths should be such thatany risk that the subject be exposed to laser light be maintained at aminimum. In fact, present laser safety regulations have set the exposurelevels based upon what can be safely tolerated by the human eye. (ACGIH(1972), American Conference of Governmental Industrial Hygienists; ANSI(1973), American National Standard for the Safe Use of Lasers).

In holographic applications, the object beam is normally expanded by theuse of lenses and then diffused by the use of ground glass screens orthe like. If the object beam is not properly expanded or diffused, itmay pose a hazard to a human subject. Also, the reference beam, whichmust be undiffused because it necessarily must have a higher energylevel to facilitate recording of a holographic image, also poses apotential threat to human subjects. Various geometries such as anoverhead reference beam give partial safety, but do not absolutelysafeguard against accidental or deliberate viewing of the reference beamby a human subject.

Another consideration when recording holographic images of humansubjects is to obtain the most lifelike reconstruction and clarity ofthe image. However, at the instant the holographic image is recorded,the room should be generally free of light sources other than the laserlight which generates the object beam and the reference beam. When usinga pulse laser to record an image, it is generally desirable for thesubject to sit in a dark room up until the moment that his image isrecorded. However, as is well known, the pupil of the eye varies indiameter in response to the illumination level. Accordingly, the priorart attempts to record holographic images of human subjects under darkroom conditions have resulted in reconstructed images whereby thesubject's pupils have been unusually large in size which is unlifelike.

Accordingly, it would be desirable to provide an apparatus and methodfor recording holograohic images in human subjects which is both safeand which results in natural and lifelike images being recorded.

This invention is directed to a method for recording lifelike images inholographic recording materials and more particularly to a methodwhereby dark eye adaptation of a human subject is minimized. Experimentshave shown that the pupil of the human subject varies within theextremes of 2 and 10 mm. When the human subject is subjected to a changeof illumination from bright to darkness, the pupil diameter will changefrom less than 3 mm to over 7 mm over a period of about 100 seconds.Tests have shown that the pupil will commence to respond to darknessafter only about 0.5 seconds. (See generally, Light Color & Vision, Vyes& Grand, Chapman & Hall, pp. 96-98). Therefore, in order to record alifelike holographic image of a human subject, when the subject isinitially illuminated with natural room light, it is necessary that therecording event take place substantially within a 0.5 second intervalafter white light illumination of the subject is terminated. It isdesirable to maintain the subject in natural room light prior to therecording event so that a holographic operator can choose the subject'sexpression under the most natural of conditions, i.e., white light.Accordingly, the present invention provides a method of recording aholographic image of a human subject which provides for illuminating thesubject in white light up to the time of the recording event, but whichalso minimizes the possibility of dark eye adaptation of the humanpupil.

When the pupil of the subject's eye is dark eye adapted (having a pupildiameter of 7 mm), the maximum permissible safety levels for aQ-switched ruby laser, based on the ACGJH 1972 and ANSI 1973 formula(Handbook of Optical Holography, Caulfield, Academic Press (1979), p.616), is I_(Rmax) 0.07 J/cm² (which resolves to I_(Dmax) =0.07 J/cm²),for the energy density incident upon the diffusing screen. However, fora daylight adapted eye having a diameter of 3 mm, this value can beincreased by a factor of 5 to 0.35 J/cm², since the I_(Dmax) =0.07 J/cm²calculation is based upon a dark adapted pupil with a diameter of 7 mm.This increased energy density on the illumination screen allows for morespot-like illumination effects as opposed to the flat diffused lightingrequired by the 0.07 J/cm² level, or on the other hand, if conventionallighting is still used, the safety factor is increased by a factor of 5.Therefore, not only do subjects with daylight adapted eyes appear morelifelike, but in addition, the energy density can be higher and still bewithin safety levels.

In accordance with the method of the present invention, the holographicrecording medium has a shutter and uses a pulse laser which generates anobject beam and reference beam. The method of recording comprises thesteps of illuminating the subject with a white light source for at leasta predetermined time period, extinguishing the white light source,opening the shutter mechanism of the holographic recording medium,activating a pulse laser having an object beam directed towards thesubject with the pulse laser positioned so that the object beam lightreflected off the subject to be directed towards the recording medium,said laser also providing a reference beam directed towards therecording medium to thereby record holographic image, and closing theshutter mechanism. It is preferred that the steps of extinguishing,opening, and activating occur within the time period of about 0.5seconds, so that dark eye adaptation of the human subject will beminimized.

By practicing the method of the present invention, the holographicoperator will know exactly the expression of the subject's face at themoment of the recording event, i.e., exposure of the holographicrecording medium, and the continuous illumination of the subject willprevent dilation of the subject's eye which would otherwise occur due todark eye adaptation. Also, by providing for the above steps to occurwithin a time period of substantially 0.5 seconds or less, not only iseye dilation minimized, but subject anxiety is lessened, which willcontribute to a more natural and lifelike image being recorded. Also, ared filter can be inserted over the white light source so that thesubject is illuminated in the same color light within which his imagewill be recorded. In this way, the holographic operator will be able tosee the subject under the same color light conditions which exist duringthe actual recording event.

Numerous other advantages and features of the present invention willbecome readily apparent when the following detailed description of theinvention and embodiments thereof, from the claims and from theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of an apparatus for recording aholographic image of a human subject having means for preventing thesubject from exposure to the reference beam;

FIG. 2A is a side elevational view of an alternative embodiment to thatshown in FIG. 1; and

FIG. 2B is top plan view of part of the embodiment of FIG. 2A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While this invention is susceptible of embodiment in many forms, thereis shown in the drawings and will herein be described in detail twospecific embodiments, with the understanding that the present disclosureis to be considered as an exemplification of the principles of theinvention and is not intended to limit the invention to the embodimentsillustrated.

Referring now to FIG. 1, there is shown a laser light source 10 which ispreferably a pulse laser. The laser source 10 emits a laser beam 12which is split by a beam splitter 14 into a reference beam 16 and objectbeam 18. A safety interlock mechanism 20a is connected in series withthe energization circuit of the pulse laser for a purpose to bedescribed below.

The reference beam 16 is expanded through negative lens 22 and passesthrough the interior region of a housing 24 wherein it is reflected offof a reflective surface 26 downwardly towards a holographic recordingmaterial 28. The recording material 28 is held by a holding means orfilm platen 32 which is pivotally adjustable as indicated to optimizethe incidence of reference and object wavefronts to create clearinterference fringes in the recording medium 28. The holding means orfilm platen 30 is covered with a light-proof film shutter 32.

The object beam 18 from beam splitter 14 is directed towards a negativelens 34 which expands the object beam and through ground glass screen 36which diffuses the object beam so as to minimize the hazard to a humansubject 38. The expanded and diffused object beam 18 passes through oneside of the protective housing 24 through a window 40 and out of theother side of the protective housing through a clear glass window 42.This object beam light is reflected off a human subject back through theclear glass window 42 and off a specially coated mirror 44 toward therecording material 28 as indicated. The specially coated mirror 44preferably functions as a two-way mirror so that an operator can viewthe human subject 38 from the opposite side of the protective housing 24from the subject. The mirror 44 is preferably coated to totally reflectlaser light of the frequency and polarization chosen at a mean angle of45° incident thereto, while being transparent to white light, therebycreating the two-way effect.

The protective housing 24 along with the clear glass window 42 serves asa safety means for preventing the human subject 38 from exposure to thereference beam 16, since the protective housing substantially enclosesthe path of the reference beam along at least a substantial portionthereof.

FIGS. 2a and 2b illustrate an alternative embodiment to that shown inFIG. 1. Here the safety means comprises means for detecting the presenceof a subject near the path of the reference beam 16, which in turncomprises a plurality of signal generating elements 50 which generatesensing signals preferably in the form of light signals. A plurality ofassociated signal detector elements 52 are spaced from and positioned toreceive the sensing signals so generated, with all of the elementspositioned along the periphery of at least a substantial portion of thereference beam path 16. If a human subject 38, or any other objectshould block the path of a sensing signal 51 from reaching a detectorelement 52, means 54 associated with the detector elements 52 produces acontrol signal indicative of a sensing signal being blocked. Thiscontrol signal is received by a safety interlock mechanism 20 whichprevents the laser from being fired in response to a control signal.Alternatively, or in combination, an occluder 20b can be provided whichwill block the path of the laser light beam 12 by the occluder's releasein response to the production of a control signal. Conventional meanssuch as a normally energized solenoid can be used to hold such anoccluder 20b above the laser beam 12 so that upon the production of acontrol signal, or upon a malfunction such as a power loss, the solenoidwill automatically de-energize and cause the occluder 20b to drop downinto the path of the laser beam 12. A safety interlock mechanism 20a maycomprise a switch in series with the circuit which fires the pulselaser, wherein the switch is opened when a control signal is produced.

A second safety means can be used for preventing the human subject 38from harmful exposure to the object beam 18. Such a second safety meansaccording to the invention comprises means for holding a ground glassscreen 36 in the path of the object beam 18 and a means for sensing thepresence of such a ground glass screen in the holding means. If theground glass screen should fail to be present in the holding means, asafety interlock mechanism 20a laser light occluder means 20b similar tothat described above for the reference beam can be provided to preventenergization of the laser source and/or block the laser light source inresponse to the sensing means failing to sense the presence of a groundglass screen.

As can be seen from FIG. 2A, the signal detector elements 54 arearranged in two groups. The elements of the first group in the upperhalf of FIG. 2A are arranged along a line passing downwardly to theright along the periphery of the path of the reference beam 16. However,since about 8 to 10 percent of the reference beam 16 reflects off theholographic recording material 28, the other elements 54 in the lowerhalf of FIG. 2A are arranged along a line passing downwardly to theleft.

The alternative embodiment in FIGS. 2A and 2B shows the holographicrecording material 28 disposed vertically and is somewhat larger thanthat of FIG. 1, in order to make larger scale holograms. However, theembodiment shown in FIG. 1 could just as well make larger scaleholograms and the embodiment shown in FIGS. 2A and 2B could just as wellmake smaller scale holograms.

As shown in FIG. 2A, a white light source 60 is shown near the negativelens 34 and ground glass screen 36 and is used for illuminating thesubject prior to the event of recording a holographic image of thesubject in accordance with the method of the present invention. Asdiscussed above, the pupil of the human eye responds to changes inintensity level of room light. By using the method according to thepresent invention, more life-like recordings of human subjects can beobtained by illuminating the human subject in white light substantiallyup to the time of the recording event.

The method comprises illuminating the subject for at least apredetermined time period so that the human subject's eyes are adaptedto the particular intensity level of the white light source. Insuccession, the white light source is extinguished, the shutter isopened, and the pulse laser is activatd to generate an object beam and areference beam. The shutter is closed after the holographic image isrecorded in the recording medium. After the shutter is closed, the humansubject is preferably reilluminated with the white light source.

Since the duration of the pulse of the pulse laser will be on the orderof 20 nano-seconds, the above sequence of steps can be performed inrapid succession almost undetectable to the human eye. Accordingly, notonly is pupil dilation of the human subject minimized, but anxiety ofthe human subject is also kept to a minimum with the overall resultbeing the recording of images having a truly lifelike quality. Suitablecontrol mechanisms can be used to control the sequence and timing ofilluminating the subject, extinguishing the white light source, openingthe shutter, activating the pulse laser, closing the shutter, andreilluminating the human subject.

Also, a red filter 62 can be provided over the white light source sothat the subject is illuminated in the same light with which his imagewill be recorded.

For the foregoing, it will be observed that numerous variations andmodifications may be effected without departing from the true spirit andscope of the novel concept of the invention. It is to be understood thatno limitation with respect to the specific apparatus or methodillustrated and described herein is intended or should be inferred. Itis, of course, intended to cover by the appended claims all suchmodifications as followed in the scope of the claims.

I claim:
 1. Method of recording a holographic image of a human subjecton a holographic recording material having a shutter, and using a pulselaser which generates an object beam and reference beam of a particularwavelength, comprising the steps of:illuminating the subject with alight source of substantially the same color as the wavelength of thelaser to thereby simulate the laser for at least a predetermined timeperiod necessary to adapt the subject's eyes to the intensity level ofthe light source: extinguishing the light source; opening the shutter;activating a pulse laser having an object beam directed toward thesubject with the pulse laser positioned so that the object beam lightreflected off the subject will be directed towards the recording medium,said laser also producing a reference beam directed towards therecording medium to thereby record a holographic image wherein the stepsof extinguishing, opening and activating are performed within a timeperiod of approximately 0.5 seconds; and closing the shutter.
 2. Methodin accordance with claim 1 further including the step of reilluminatingthe human subject with the light source after the step of closing theshutter.
 3. Method in accordance with claim 1 wherein the light sourceis a white light source having a red filter.